linux-kernel - [PATCH V3 14/14] kvm: x86/mmu: Skip calling mmu->sync

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Date:   Fri, 17 Feb 2023 07:53:21 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org
Subject: [PATCH V3 14/14] kvm: x86/mmu: Skip calling mmu->sync_spte() when the spte is 0

From: Lai Jiangshan <jiangshan.ljs@...group.com>

Sync the spte only when the spte is set and avoid the indirect branch.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
---
 arch/x86/kvm/mmu/mmu.c         | 4 ++--
 arch/x86/kvm/mmu/paging_tmpl.h | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index a8ac37d51287..cd8c38463c97 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1942,7 +1942,7 @@ static int __kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 		return -1;
 
 	for (i = 0; i < SPTE_ENT_PER_PAGE; i++) {
-		int ret = vcpu->arch.mmu->sync_spte(vcpu, sp, i);
+		int ret = sp->spt[i] ? vcpu->arch.mmu->sync_spte(vcpu, sp, i) : 0;
 
 		if (ret < -1)
 			return -1;
@@ -5764,7 +5764,7 @@ static void __kvm_mmu_invalidate_addr(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu
 	for_each_shadow_entry_using_root(vcpu, root_hpa, addr, iterator) {
 		struct kvm_mmu_page *sp = sptep_to_sp(iterator.sptep);
 
-		if (sp->unsync) {
+		if (sp->unsync && *iterator.sptep) {
 			/*
 			 * Get the gfn beforehand for later flushing.
 			 * Although mmu->sync_spte() doesn't change it, but just
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index e04950015dc4..3373d6705634 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -933,7 +933,7 @@ static int FNAME(sync_spte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, int
 	gpa_t pte_gpa;
 	gfn_t gfn;
 
-	if (!sp->spt[i])
+	if (WARN_ON_ONCE(!sp->spt[i]))
 		return 0;
 
 	first_pte_gpa = FNAME(get_level1_sp_gpa)(sp);
-- 
2.19.1.6.gb485710b